The present invention relates to the hydrodynamics of marine vessels, more particularly to adjuncts, appendages and auxiliary devices for affecting same.
Structural additions of various kinds and configurations have been implemented for various types of marine vessels in order to improve powering performance. Some very small pleasure craft and planing boats have been provided with adjustable trim flaps (trim tabs) for controlling the trim. As for combatant vessels, during World War II some small German ships were provided with stern wedges for the purpose of improving powering performance. Until the early 1980's, however, neither stern wedges nor stern flaps were known to be pursued by anyone for combatant ships of the frigate/destroyer size (approximately 3,000 to 10,000 Long Tons displacement).
In the 1980's some foreign navies began to successfully apply stern wedges to larger ships up to the frigate size. In addition, the U.S. Navy began to explore possibilities regarding auxiliary structure for enhancing powering performance of larger (frigate/destroyer sized) ships. See Righter, J. R., Jr. and R. Compton, "The Effects of a Bow bulb and Stern Wedge on a Large Waterplane, Transom Sterned Hullform," U.S. Naval Academy Report, EW-25-82 (October 1982), incorporated herein by reference; Karafiath, G. and S. C. Fisher, "The Effect of Stern Wedges on Ship Powering Performance," Naval Engineers Journal (May 1987), incorporated herein by reference. Based on the research efforts presented in the paper by Karafiath and Fisher, supra, the U.S. Navy designed the Arleigh Burke (DDG 51) Class destroyer with a stern wedge inlaid into the hull; many of these twenty-seven designed DDG 51's are already built. Model tests demonstrated that implementation of such a stern wedge resulted in a reduction of power of up to a maximum of about 6% at speeds above 24 knots.
A stern wedge design was initially attempted by the U.S. Navy for the FFG 7 frigate class; however, in the course of model testing it was discovered that a stern flap was more effective than a stern wedge on this class. The model tests demonstrated approximately a 5% decrease in delivered power at speeds of 20 knots and above. In 1989, a stern flap was designed and retrofitted by the U.S. Navy on the USS Copeland frigate (FFG 25). Analysis of the ship trials data for the USS Copeland frigate having a retrofitted stern flap indicated an 8% power saving, somewhat greater than the model test results, and increased top end speed. See Cusanelli, D. S., and W. M. Cave, III, "Effect of Stern Flaps on Powering Performance of the FFG-7 Class," Marine Technology, Vol. 30, No. 1 (January 1993), incorporated herein by reference.
A stern flap design was selected through model testing for full scale retrofit to the PC 1 Class Patrol Coastal. The retrofit of a stern flap on the Shamal (PC 13) showed that the flap would reduce required delivery power by 5.6% and increase top speed and range on this class. See Cusanelli, D. S., "Stern Flap Powering Performance on the PC 1 Class Patrol coastal, Full Scale Trials and Model Experiments," PATROL '96 Conference, New Orleans, La. (December 1996), incorporated herein by reference. Subsequent to the above-noted investigation regarding the Shamal, the U.S. Navy has tested various stern flaps at CDNSWC on several models of various ship types. These model tests have not only shown that significant energy savings are possible with stern flaps, but have also provided valuable insights into stern flap operational mechanisms. See, e.g., the paper by Cusanelli (December 1996), supra; Cusanelli, D. S., and K. M. Forgach, "Stern Flaps for Enhanced Powering Performance," Twenty-Fourth American Towing Tank Conference, College Station, Tex. (November 1995), incorporated herein by reference.
Although the aforedescribed results have been encouraging, the U.S. Navy has continued to seek better ways for improving ship powering performance.